In its perpetual struggle against sickness and disease, humankind needs rapid and inexpensive means of detecting biological molecules responsible for human infirmities. Modern man faces a gamut of threats to human health, including biological warfare, emerging drug-resistant forms of infectious diseases, rising incidences of food contamination by pathogenic bacteria, infectious diseases in underdeveloped countries, and manmade environmental hazards. There is a sense of urgency to find appropriate technological solutions for diagnosing and monitoring biological threats to human health. Progress in biomedical assays, diagnostics and biological science, however, often encounters an inability to process large numbers of samples with a satisfactory degree of throughput.
Microfluidics devices have become a potential source of hope in meeting the needs for high-throughput measurements. Microfluidics possesses the potential for high throughput, rapid reaction kinetics, and small sample consumption. Industry has produced many types of microfluidic devices, typically using electrophoretic or electroosmotic forces to move small fluid volumes. Current approaches to microfluidic control include lateral flow structures, electrophoretic methods, and pneumatic designs. Each of these approaches has certain limitations that have slowed the pace of microfluidics-device development, such as problems with scaling, assay reconfigurations, poor sample-use efficiency, and considerable complexity of circuitry.
Lateral flow structures, for example, that rely on microporous membranes have properties and performance that are difficult to control. Electrophoretic methods for controlling the flow of fluid are not compatible with many solvents, and can result in the separation of biological molecules during steps when solution homogeneity is desired. Further, voltage leakage between microfluidic channels can limit the precision with which the methods can control the flow of fluid. Pneumatic designs have been successfully implemented using soft-lithography techniques, but these implementations are limited to elastomer materials that are not compatible with many types of biological assays. Some lithographic methods produce fixed networks of microconduits (i.e., micropipes) that make reconfiguration difficult and, in effect, result in single-use devices. There is, therefore, a need for microfluidics apparatus and techniques that can avoid or mitigate the aforementioned disadvantages of such current approaches.